1. Technical Field
The present invention relates to an image processing apparatus, an image processing method and a computer-readable medium storing a program that causes a computer to execute image processing.
2. Related Art
A color scan image is not suitable for storage or transmission because it has the size of tens of megabytes. For this reason, a pixel block including a character, a line image, and the like is handled as a binary image with color information and the like and is subjected to lossless compression, such as MMR (Modified Modified Read), while JPEG (Joint Photographic Experts Group) compression is performed for graphics or a natural image with being handled as a multilevel image. In addition, there is proposed a method of adding an extended character, an extended line image, and the like onto an extended JPEG image using attached color information when reproduced is an image which is compressed by the above-described manner.
In this case, for example, in a character within an image, a color of a peripheral portion of the character may be changed due to deterioration of an MTF (Modulation Transfer Function) caused by scanner reading, a JPEG compression immediately after the scan, and the like. More specifically, a character periphery may be blurred, a background color and a character color may run, or pixels in which a character color changes may occur depending on the parameters of the JPEG compression. In such a case, it has been desired to reproduce an original color.
As the related techniques, for example, JP 2004-128880 A has an object to provide an image compression apparatus, an image extension apparatus, a method thereof, and a program that can generate a good restored image and can perform image compression without degrading a quality of a compressed image. A binarization section binarizes a multilevel image. A region specifying section A specifies a position of a character region within the binary image. A region specifying section B specifies a position of a unit character region within the character region. A representative color portion extracting section extracts a representative color of the unit character region based on position information of the unit character region and the multilevel image. A character region filling section fills the character region with a peripheral color based on the position information of the character region. A reduction section reduces the filled multilevel image. A JPEG compression section compresses the reduced multilevel image. An MMR compression section compresses a partial binary image corresponding to the character region and outputs compression data including the positional information, a compression code generated by each compression section, and representative color information of the unit character region.
Furthermore, for example, JP 2000-357230 A has an object to reduce an error in region division for a boundary edge portion or the like between a background portion and a character portion of a color document image and to improve an accuracy of character extraction and the like. A color image is input through an image input section. A used color specifying section specifies colors to be used. A region creating section creates a region for each of the specified colors to be used. A region color correcting section corrects allocation of a use color to a region in interest based on a positional relationship in color space between a use color allocated to the region in interest and a use color allocated to an adjacent region to the region interest. A character extracting section extracts a character within the color image using information on the region for each use color.
Furthermore, for example, JP Hei. 5-62013 A describes that its most significant feature is to make it possible to easily extract only characters from a three-color printed material in which the characters expressed with a first color are printed while overlapping patterns expressed with second and third colors. In this configuration, a CPU calculates parameters for density conversion based on RGB values of a background color of a material to be read which are input through a data input circuit and RGB values of first and second patterns to be removed which are input through the data input circuit. The calculated parameters are written in advance into a look-up table circuit, and image signals collected from the material to be read are converted into a gradation image in which only the characters are extracted in accordance with the parameters. Then, the obtained image is converted into a binary image in a binarization circuit for output.
Furthermore, for example, JP 2008-99149 A has an object to easily and highly accurately detect colors of characters. An MFP includes: a character region extracting section that extracts a character region with a character attribute, in which a character is expressed, from a color image; a line thinning section that makes a character included in the character region thinner; a character color determining section that determines a character color based on colors of pixels of a color image corresponding to plural character pixels which form a middle of the thinned character; a noise eliminating section that converts the color image into a binary image by binarizing the color image; a character region encoding section that encodes the character region of the binary image and generates code data; and an integration section that associates the generated code data, the determined character color, and the position of the character region in the color image.
Furthermore, for example, JP 2004-242075 A has an object to accurately extract a character color and character region information in a multilevel image by feedback of the color extraction result to character clipping processing. An image processing apparatus includes: character region image generating means for generating a binary image of a character region from a color image; characters clipping means for generating a character rectangle for the binary image of the character region; one-color determination means for performing one-color determination of the character rectangle; means for determining as to whether or not a non-one-color character rectangle is a group of plural kinds of one-color characters; and detailed character clipping means for performing character clipping within the determined rectangle.
Furthermore, for example, JP Hei. 5-130426 A has an object to provide an image processing apparatus capable of highly efficiently encoding and decoding an image. An edge detecting section detects an edge of an image. A first color detecting section detects a predetermined color. A first color character extracting section to which the detection result is input extracts a skeleton portion of a color character. Then, a second color detecting section detects a color around pixels detected as the color character. A second color character extracting section receives a color character attached to the skeleton of the color character extracted by the first color character extracting section according to the result. Then, a thin line detecting section determines it to be a thin line portion of the color character when an edge pixel has a predetermined color. A mixing section mixes it with the color character from the second color character extracting section, and it is finally output as the color character.
Furthermore, for example, JP 2007-249774 A has an object to accurately determine a color of a character expressed by a character image input through a scanner or the like. An image forming apparatus is provided with: a thinned image generating section that detects a middle line of a linear figure of a character expressed in a scan input image and a middle region, which is a region around the middle line, by generating a thinned image of the input image; a character image dividing section that divides the middle region into plural character color candidate regions RC; an approximate color pixel selecting section that detects a pixel, which meets a predetermined condition, among pixels belonging to small regions as an approximate color pixel for each of the small regions; and a character color determining section that determines a color of the character expressed in the input image based on color information of the pixel, meeting the predetermined condition, of each small region.